Piston destruction issues

barnett468
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barnett468 12/7/2018 1:46pm
12/7/2018 1:46pm
riv187 wrote:
The ring is the conductor of heat from piston top out to cylinder,,,when it stuck and jambed into ring land,,heat spiked on top leading to the...
The ring is the conductor of heat from piston top out to cylinder,,,when it stuck and jambed into ring land,,heat spiked on top leading to the specs in chamber. Then the piston snagged the exhaust port as it was able to rock more and the intake skirt slammed other side and broke simultanously. This is what I think happened in a less than a secound or 2. It was a chain reation.You may find .003" play in lower rod bearing,,.005" in main,,.005 in wrist pin,,Gasket was a little thinner,piston stuck up a little more than stock,,head surface before.010 and bingo it all stacked up to kiss the head.
m1ke20012 wrote:
Indeed
no, not indeed. that is simply a theory. the only way to know with more certainty is to measure the squish clearance with the damaged piston.
m1ke20012
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m1ke20012 12/7/2018 2:19pm
12/7/2018 2:19pm
riv187 wrote:
The ring is the conductor of heat from piston top out to cylinder,,,when it stuck and jambed into ring land,,heat spiked on top leading to the...
The ring is the conductor of heat from piston top out to cylinder,,,when it stuck and jambed into ring land,,heat spiked on top leading to the specs in chamber. Then the piston snagged the exhaust port as it was able to rock more and the intake skirt slammed other side and broke simultanously. This is what I think happened in a less than a secound or 2. It was a chain reation.You may find .003" play in lower rod bearing,,.005" in main,,.005 in wrist pin,,Gasket was a little thinner,piston stuck up a little more than stock,,head surface before.010 and bingo it all stacked up to kiss the head.
m1ke20012 wrote:
Indeed
barnett468 wrote:
no, not indeed. that is simply a theory. the only way to know with more certainty is to measure the squish clearance with the damaged piston.
Good idea, I shall do such.
project racer 12/7/2018 2:49pm
12/7/2018 2:49pm Edited Date/Time 12/7/2018 2:57pm
If that is a Namura piston, part of the problem is right there.
project racer 12/7/2018 2:53pm
12/7/2018 2:53pm Edited Date/Time 12/7/2018 3:43pm
Once the piston to bore clearance gets excessive, the heat factor goes way up, as the piston is unable to transfer heat away to the bore, and on to the cylinder casting . Looks like some scuff / seizure marks on the intake side of the piston. A loose bore will seize as well as a tight one. Being an '03, that cylinder is probably way out of spec. Only piston that ever broke a skirt on me was when a new piston was installed in a used bore. It ran for about 6-8 hours before it shattered the intake skirt off. Piston rock / loose bore.

Yeah, the piston may have kissed the head. After it was in pieces. Could have very easily shot a chunk of broken piston through the transfer ports, and wedged on top of the piston as it struck the head.

The Shop

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dkurtd
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dkurtd 12/7/2018 3:33pm
12/7/2018 3:33pm
You have more theories out there than the D.B Cooper case. You will probably never fully know. And all you're going to get here is theories.

My advice start from scratch and with clean cases, a good crank/rod (I would recommend splitting the cases), and a better quality piston. Ensure the cylinder is in good shape and that you have proper piston/cylinder clearance. Check squish, change the fuel and definitely check your jetting against stock numbers.

There are plenty of quality companies that can rebuild your crank if need be and also replate your cylinder all at reasonable prices. Good luck.

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m1ke20012
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m1ke20012 12/7/2018 5:01pm
12/7/2018 5:01pm
dkurtd wrote:
You have more theories out there than the D.B Cooper case. You will probably never fully know. And all you're going to get here is theories...
You have more theories out there than the D.B Cooper case. You will probably never fully know. And all you're going to get here is theories.

My advice start from scratch and with clean cases, a good crank/rod (I would recommend splitting the cases), and a better quality piston. Ensure the cylinder is in good shape and that you have proper piston/cylinder clearance. Check squish, change the fuel and definitely check your jetting against stock numbers.

There are plenty of quality companies that can rebuild your crank if need be and also replate your cylinder all at reasonable prices. Good luck.

Suggestions for replating companies?
dkurtd
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dkurtd 12/7/2018 5:08pm
12/7/2018 5:08pm
dkurtd wrote:
You have more theories out there than the D.B Cooper case. You will probably never fully know. And all you're going to get here is theories...
You have more theories out there than the D.B Cooper case. You will probably never fully know. And all you're going to get here is theories.

My advice start from scratch and with clean cases, a good crank/rod (I would recommend splitting the cases), and a better quality piston. Ensure the cylinder is in good shape and that you have proper piston/cylinder clearance. Check squish, change the fuel and definitely check your jetting against stock numbers.

There are plenty of quality companies that can rebuild your crank if need be and also replate your cylinder all at reasonable prices. Good luck.

m1ke20012 wrote:
Suggestions for replating companies?
Millennium Technologies have done mine. https://www.millennium-tech.net/
2
buzzlight52
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buzzlight52 12/26/2018 8:55pm
12/26/2018 8:55pm
m1ke20012 wrote:
Can anyone tell what is causing this? This has happened twice. I got the bike like such and then Replaced the top end for it to...
Can anyone tell what is causing this? This has happened twice. I got the bike like such and then Replaced the top end for it to do it again 4 hours later. I was told it could be detonation and running lean. Bike is an 03 yz125.


My Yz 250 just did the same thing. Intake side skirt shattered and totally destroyed the skirt on my cylinder. I have been told since it is because of the hole on the intake side of the piston that can cause excessive wear when ran too lean. Gonna change a top end about every 30 hours now since this
40acres
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40acres 12/27/2018 9:44am
12/27/2018 9:44am
project racer wrote:
If that is a Namura piston, part of the problem is right there.
This is false.
Tracktor
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Tracktor 12/27/2018 10:33am
12/27/2018 10:33am
project racer wrote:
If that is a Namura piston, part of the problem is right there.
40acres wrote:
This is false.
Lol, no. No it isn't. Namura is crap. Oh sure plenty of people have used and not had issues but you are paying russian roulette with your engine using one. All to save a massive $20. That said, use whatever you want but know that no decent engine builder uses Namura pistons...........
40acres
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40acres 12/27/2018 10:59am
12/27/2018 10:59am
Sure bud, very nice opinion you have there.

Pit Row

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